U.S. patent application number 13/980218 was filed with the patent office on 2013-11-07 for reserving transmission resources in wireless network.
This patent application is currently assigned to Nokia Corporation. The applicant listed for this patent is Jarkko Kneckt, Eng Hwee Ong. Invention is credited to Jarkko Kneckt, Eng Hwee Ong.
Application Number | 20130294394 13/980218 |
Document ID | / |
Family ID | 46636798 |
Filed Date | 2013-11-07 |
United States Patent
Application |
20130294394 |
Kind Code |
A1 |
Kneckt; Jarkko ; et
al. |
November 7, 2013 |
RESERVING TRANSMISSION RESOURCES IN WIRELESS NETWORK
Abstract
Methods, apparatuses, and a computer program are presented for
determining a reservation period for data transmission in a
wireless communication network. The duration of the reservation
period is determined on the basis of RTS/CTS handshake between a
transmitter and a receiver apparatus.
Inventors: |
Kneckt; Jarkko; (Espoo,
FI) ; Ong; Eng Hwee; (Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kneckt; Jarkko
Ong; Eng Hwee |
Espoo
Singapore |
|
FI
SG |
|
|
Assignee: |
Nokia Corporation
Espoo
FI
|
Family ID: |
46636798 |
Appl. No.: |
13/980218 |
Filed: |
February 15, 2011 |
PCT Filed: |
February 15, 2011 |
PCT NO: |
PCT/FI11/50141 |
371 Date: |
July 17, 2013 |
Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 84/12 20130101;
H04W 74/004 20130101; H04W 72/04 20130101; H04W 74/0816 20130101;
H04W 74/006 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 72/04 20060101
H04W072/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2011 |
US |
13026426 |
Claims
1-27. (canceled)
28. A method, comprising: causing the wireless communication
apparatus to transmit a transmission request message to a second
wireless communication apparatus on a plurality of channels,
wherein the transmission request message is used to query whether
or not at least one of said plurality of channels is free, and
wherein the transmission request message triggers a first
reservation period to said plurality of queried channels; receiving
a transmission response message as a response to the transmission
request message, wherein the transmission response message
indicates at least one channel the second wireless communication
apparatus has detected to be free; determining the duration of a
second reservation period on the basis of the received transmission
response message, wherein the second reservation period extends to
cover data transmission; and causing the wireless communication
apparatus to reserve said at least one channel detected to be free
for the second reservation period and to transmit data during the
second reservation period.
29. The method of claim 28, wherein the determined duration of the
second reservation period is longer in a case where at least one of
said plurality of queried channels is detected not to be free than
in a case where said plurality of queried channels are all detected
to be free.
30. The method of claim 28, wherein the transmission of the
transmission request message and the reception of the transmission
response message are carried out during a probing phase, wherein
the duration of the first reservation period is confined to the
probing phase, and wherein the duration of the second reservation
period extends to protect said data transmission.
31. The method of claim 28, further comprising: in response to the
reception of the transmission response message indicating the free
channels, determining on the basis of the number of free channels
whether or not to proceed to the data transmission and to carry out
the channel reservation and determining the duration of the second
reservation period.
32. The method of claim 28, further comprising: computing the
duration of the second reservation period on the basis of the
number of channels detected to be free with respect to the number
of said plurality of channels on which the transmission request
message was transmitted; causing the wireless communication
apparatus to transmit a second transmission request message
comprising an information element defining the duration of the
second reservation period; receiving a second transmission response
message from the second wireless communication apparatus in
response to the second transmission request message; and upon
reception of the second transmission response message, causing the
transmitter to transmit data to the receiver during the second
reservation period.
33. The method of claim 28, further comprising: reading the
duration of the second reservation period from the received
transmission response message; computing a currently remaining
duration of the second reservation period; and causing the wireless
communication apparatus to transmit another transmission response
message destined to the wireless communication apparatus itself and
comprising an information element defining the remaining duration
of the second reservation period, thereby affecting reservation of
said free channels in a coverage area of the wireless communication
apparatus.
34. A method, comprising: receiving, in a wireless communication
apparatus, a transmission request message on at least one channel,
wherein the transmission request message is used to query whether
or not at least one of a plurality of channels queried with the
transmission request message is free, and wherein the transmission
request message triggers a first reservation period to said
plurality of channels; determining the duration of a second
reservation period, wherein the second reservation period extends
to cover a data transmission and is longer in a case where at least
one of said plurality of queried channels is detected not to be
free than in a case where said plurality of queried channels are
all detected to be free; causing the wireless communication
apparatus to transmit a transmission response message as a response
to the transmission request message, wherein the transmission
response message indicates at least one channel detected to be
free.
35. The method of claim 28, wherein the reception of the
transmission request message and the transmission of the
transmission response message are carried out during a probing
phase, wherein the duration of the first reservation period is
confined to the probing phase, and wherein the duration of the
second reservation period extends to protect the data
transmission.
36. The method of claim 28, further comprising: computing the
duration of the second reservation period on the basis of the
number of channels detected to be free with respect to the number
of said plurality of channels queried with the transmission request
message; transmitting in the reservation response message an
information element defining the duration of the computed second
reservation period.
37. An apparatus comprising: at least one processor; and at least
one memory including a computer program code, wherein the at least
one memory and the computer program code are configured, with the
at least one processor, to cause the apparatus to: cause a first
wireless communication apparatus to transmit a transmission request
message to a second wireless communication apparatus on a plurality
of channels, wherein the transmission request message is used to
query whether or not at least one of said plurality of channels is
free, and wherein the transmission request message triggers a first
reservation period to said plurality of queried channels; receive a
transmission response message as a response to the transmission
request message, wherein the transmission response message
indicates at least one channel the second wireless communication
apparatus has detected to be free; determine the duration of a
second reservation period on the basis of the received transmission
response message, wherein the second reservation period extends to
cover data transmission; and cause the first wireless communication
apparatus to reserve said at least one channel detected to be free
for the second reservation period and to transmit data during the
second reservation period.
38. The apparatus of claim 37, wherein the determined duration of
the second reservation period is longer in a case where at least
one of said plurality of queried channels is detected not to be
free than in a case where said plurality of queried channels are
all detected to be free.
39. The apparatus of claim 37, wherein the at least one memory and
the computer program code are configured, with the at least one
processor, to cause the apparatus to carry out the transmission of
the transmission request message and the reception of the
transmission response message during a probing phase, wherein the
duration of the first reservation period is confined to the probing
phase, and wherein the duration of the second reservation period
extends to protect said data transmission.
40. The apparatus of claim 37, wherein the at least one memory and
the computer program code are configured, with the at least one
processor, to cause the apparatus to, in response to the reception
of the transmission response message indicating the free channels,
determine on the basis of the number of free channels whether or
not to proceed to the data transmission and to carry out the
channel reservation and determining the duration of the second
reservation period.
41. The apparatus of claim 37, wherein the at least one memory and
the computer program code are configured, with the at least one
processor, to: cause the apparatus to compute the duration of the
second reservation period on the basis of the number of channels
detected to be free with respect to the number of said plurality of
channels on which the transmission request message was transmitted;
cause the first wireless communication apparatus to transmit a
second transmission request message comprising an information
element defining the duration of the second reservation period, to
receive a second transmission response message from the second
wireless communication apparatus in response to the second
transmission request message; and upon reception of the second
transmission response message, cause the first wireless
communication apparatus to transmit data to the receiver during the
second reservation period.
42. The apparatus of claim 37, wherein the at least one memory and
the computer program code are configured, with the at least one
processor, to cause the apparatus to read the duration of the
second reservation period from the received transmission response
message; compute a currently remaining duration of the second
reservation period; and cause the first wireless communication
apparatus to transmit another transmission response message
destined to the wireless communication apparatus itself and
comprising an information element defining the remaining duration
of the second reservation period, thereby affecting reservation of
said free channels in a coverage area of the first wireless
communication apparatus.
43. An apparatus comprising: at least one processor; and at least
one memory including a computer program code, wherein the at least
one memory and the computer program code are configured, with the
at least one processor, to cause the apparatus to: receive a
transmission request message on at least one channel, wherein the
transmission request message is used to query whether or not at
least one of a plurality of channels queried with the transmission
request message is free, and wherein the transmission request
message triggers a first reservation period to said plurality of
channels; determine the duration of a second reservation period,
wherein the second reservation period extends to cover a data
transmission and is longer in a case where at least one of said
plurality of queried channels is detected not to be free than in a
case where said plurality of queried channels are all detected to
be free; causing a wireless communication apparatus to transmit a
transmission response message as a response to the transmission
request message, wherein the transmission response message
indicates at least one channel detected to be free.
44. The apparatus of claim 43, wherein the at least one memory and
the computer program code are configured, with the at least one
processor, to cause the apparatus to carry out the reception of the
transmission request message and the transmission of the
transmission response message during a probing phase, wherein the
duration of the first reservation period is confined to the probing
phase, and wherein the duration of the second reservation period
extends to protect the data transmission.
45. The apparatus of claim 43, wherein the at least one memory and
the computer program code are configured, with the at least one
processor, to cause the apparatus to: compute the duration of the
second reservation period on the basis of the number of channels
detected to be free with respect to the number of said plurality of
channels queried with the transmission request message; cause the
wireless communication apparatus to transmit in the reservation
response message an information element defining the duration of
the computed second reservation period.
46. The apparatus of claim 43, wherein the at least one memory and
the computer program code are configured, with the at least one
processor, to cause the apparatus to: receive in the transmission
request message an information element commanding the wireless
communication apparatus to compute the second reservation period;
in response to the reception said command, compute the second
reservation period and causing the wireless communication apparatus
to transmit the transmission response message defining the duration
of the second reservation period.
47. The apparatus of claim 37, further comprising radio interface
components providing the apparatus with radio communication
capability.
Description
FIELD
[0001] The invention relates to the field of wireless
telecommunications and, particularly, to reserving transmission
resources in a wireless communication system.
BACKGROUND
[0002] Wireless Local Area Network (WLAN) has undergone vast
development in order to increase throughput. Task groups such as
802.11b, 802.11a, 802.11g and 802.11n have demonstrated continuous
improvement of the WLAN radio throughput. 802.11ac is another task
group that is developing the WLAN radios that operate at a
frequency spectrum below 6 GHz and especially at 5 GHz. There exist
other task groups within the IEEE 802.11 standardization.
BRIEF DESCRIPTION
[0003] According to an aspect of the present invention, there are
provided methods as specified in claims 1 and 7.
[0004] According to another aspect of the present invention, there
are provided apparatuses as specified in claims 13 and 19.
[0005] According to another aspect of the present invention, there
is provided an apparatus as specified in claim 26.
[0006] According to yet another aspect of the present invention,
there is provided a computer program product embodied on a computer
readable distribution medium as specified in claim 27. According to
yet another aspect, there is provided a computer-readable
distribution medium comprising the computer program product.
[0007] Embodiments of the invention are defined in the dependent
claims.
LIST OF DRAWINGS
[0008] Embodiments of the present invention are described below, by
way of example only, with reference to the accompanying drawings,
in which
[0009] FIGS. 1A and 1B illustrate an example of a wireless
communication system to which embodiments of the invention may be
applied;
[0010] FIGS. 2A and 2B illustrate a flow diagram of a process
according to an embodiment of the invention;
[0011] FIGS. 3 to 7 illustrate embodiments for carrying out a
channel query procedure and computing a reservation period for
subsequent data transmission according to some embodiments of the
invention;
[0012] FIGS. 8A and 9A illustrate flow diagrams of processes for
carrying out the channel query during a probing phase;
[0013] FIGS. 8B and 9B illustrate flow diagrams of processes for
computing the duration of the reservation period; and
[0014] FIG. 10 illustrates a block diagram of an apparatus
according to an embodiment of the invention.
DESCRIPTION OF EMBODIMENTS
[0015] The following embodiments are exemplary. Although the
specification may refer to "an", "one", or "some" embodiment(s) in
several locations, this does not necessarily mean that each such
reference is to the same embodiment(s), or that the feature only
applies to a single embodiment. Single features of different
embodiments may also be combined to provide other embodiments.
Furthermore, words "comprising" and "including" should be
understood as not limiting the described embodiments to consist of
only those features that have been mentioned and such embodiments
may contain also features/structures that have not been
specifically mentioned.
[0016] A general architecture of a wireless telecommunication
system to which embodiments of the invention may be applied is
illustrated in FIG. 1A. FIG. 1A illustrates two groups of wireless
communication devices forming two basic service sets, i.e. groups
of wireless communication devices comprising an access point (AP)
100, 112 and terminal stations (STA) 102, 104, 110, 114
communicating with the access points 100, 112 of their respective
groups. A basic service set (BSS) is a basic building block of an
IEEE 802.11 wireless local area network (WLAN). The most common BSS
type is an infrastructure BSS that includes a single AP together
with all associated STAB. The AP may be a fixed AP as AP 112, or it
may be a mobile AP as AP 100. The APs 100, 112 may also provide
access to other networks, e.g. the Internet 120. In another
embodiment, at least one of the BSSs is an independent BSS (IBSS)
or a mesh BSS (MBSS) without a dedicated AP, and in such
embodiments the communication device 100 may be a non-access-point
terminal station. While embodiments of the invention are described
in the context of the above-described topologies of IEEE 802.11
and, particularly, IEEE 802.11ac, it should be appreciated that
other embodiments of the invention are applicable to networks based
on other specifications, e.g. other versions of the IEEE 802.11,
WiMAX (Worldwide Interoperability for Microwave Access), UMTS LTE
(Long-term Evolution for Universal Mobile Telecommunication
System), and other networks having cognitive radio features, e.g.
transmission medium sensing features and adaptiveness to coexist
with radio access networks based on different specifications and/or
standards.
[0017] The 802.11n specifies a data transmission mode that includes
20 MHz wide primary and secondary channels. The primary channel is
used in all data transmissions, and with clients supporting only
the 20 MHz mode. A further definition in 802.11n is that the
primary and secondary channels are adjacent. The 802.11n
specification also defines a mode in which a STA can have only one
secondary channel which results in a maximum bandwidth of 40 MHz.
IEEE 802.11ac task group extends such an operation model to provide
for wider bandwidths by increasing the number of secondary channels
from 1 up to 7, thus resulting in bandwidths of 20 MHz, 40 MHz, 80
MHz, and 160 MHz. FIG. 1B illustrates an exemplary channel
structure for 20 MHz, 40 MHz, 80 MHz, and 160 MHz channels. In this
example, a 40 MHz transmission band is formed by two contiguous 20
MHz bands (denoted by numerals 1 and 2 in FIG. 1B), and an 80 MHz
transmission band is formed by two contiguous 40 MHz bands
(numerals 1, 2, 3). However, a 160 MHz band may be formed by two
contiguous (numerals 1 to 4) or non-contiguous 80 MHz bands
(numerals 1 to 3 for a first 80 MHz band and any one of bands
denoted by numerals 5 and 6 for a second 80 MHz band).
[0018] As mentioned above, the transmission band of a BSS contains
the primary channel and zero or more secondary channels. The
secondary channels may be used to increase data transfer capacity
of the TXOP. The secondary channels may be called a secondary
channel, a tertiary channel, a quaternary channel, etc. The primary
channel may be used for channel contention, and a transmission
opportunity (TXOP) may be gained after successful channel
contention on the primary channel. Every STA is reducing a backoff
value while the primary channel is sensed to be idle for a certain
time interval, for instance 9 microseconds. When the backoff
reaches zero, the STA gains the TXOP and starts transmission. If
another STA gains the TXOP before that, the channel sensing is
suspended, and the STA proceeds with the channel sensing after the
TXOP of the other STA has ended. The time duration (the backoff
factor) may not be reset at this stage, and the time duration that
already lapsed before the suspension is also counted, which means
that the STA now has a higher probability of gaining the TXOP. A
secondary channel may be used in the transmission if it has been
free for a determined time period (may be the same or different
time period than that used for gaining the TXOP) just before TXOP
start time in order for the contending STA to take the secondary
channel in use.
[0019] A virtual carrier sensing function is provided by the
provision of a network allocation vector (NAV) which is used to
reserve a channel. Most of the transmitted frames comprise a
duration field which can be used to reserve the medium (or provide
duration of the NAV protection) for the duration indicated by the
value of the duration field. In practice, the NAV is a timer that
indicates the amount of time the medium will be reserved. In a
typical operation, the transmitting and receiving stations (STAB)
will set the NAV to the time for which they expect to use the
medium while other STAB count down from the NAV to zero before
starting the channel contention. The virtual carrier sensing
function indicates that the medium is busy when NAV is non-zero and
idle when NAV is zero. The NAV may be set to protect frames
communicated on the primary channel of the BSS.
[0020] A TXOP holder (a wireless communication apparatus that has
won the channel contention) may probe for available channels in the
location of the receiver through a query procedure. During the
query procedure, the TXOP holder transmits a transmission request
message, e.g. a Request-to-Send message, to the receiver on every
channel included in the query, and the receiver responds with a
transmission response message, e.g. a Clear-to-Send message, on the
channels it detects to be free. The CTS message is a response to
the RTS message, and it may also be used to set the NAV protection.
The CTS message also comprises a duration field used in a similar
manner as with the RTS message. Then, the TXOP holder may carry out
the transmission on the free channels. The transmission request
message and/or the transmission response message may be used to set
the NAV protection. FIGS. 2A and 2B illustrate embodiments for
computing a reservation period, e.g. the NAV duration, for the TXOP
on the basis of the RTS/CTS handshake procedure. FIG. 2A
illustrates a procedure where a wireless communication apparatus
transmits one or more RTS messages and computes the reservation
period, and FIG. 2B illustrates a procedure where a receiver of the
RTS message computes the reservation period.
[0021] Referring to FIG. 2A, the process starts in block 200. In
block 202, a wireless communication apparatus has reduced the
backoff factor to zero and, thus is able to gain the TXOP. For that
purpose, the wireless communication apparatus is caused to transmit
a transmission request message to a second wireless communication
apparatus on a plurality of channels at a beginning of the TXOP.
The transmission request message is used to query whether or not at
least one of said plurality of channels is free, and the
transmission request message may be used to trigger a first
reservation period to said plurality of channels. The first
reservation period may be a short probing duration having a length
less than or equal to CTS_Timeout parameter plus the duration of at
least a following message in the IEEE 802.11ac network, or it may
have another duration. The transmission request message may be the
RTS message comprising a duration field that sets the NAV on the
channels on which the RTS is transmitted. The RTS may be
transmitted as a result of channel sensing, e.g. through
clear-channel assessment (CCA), on those channels detected to be
free (idle) in the wireless communication apparatus. In block 204,
the wireless communication apparatus receives a transmission
response message as a response to the transmission request message
from the second wireless communication apparatus. The transmission
response message indicates the channel(s) on which the RTS message
was received and detected to be free by the second wireless
communication apparatus through the CCA, for example. As a
consequence, the RTS/CTS handshake enables determination of the
channel(s) that are free around both the transmitter and the
receiver. When the duration field of the RTS frame contains a short
probing duration, the NAV reservation enables the wireless
communication apparatus gaining the TXOP to proceed with a longer
reservation or to discontinue the TXOP and free the channel access
to other device with a minimum unnecessary duration of channel
reservation. This will be discussed in greater detail below.
[0022] In block 206, duration for a second reservation period is
computed in the wireless communication apparatus on the basis of
the number of channels indicated to be free in the transmission
response message with respect to the number or a subset of said
plurality of channels on which the transmission request message was
transmitted. The second reservation period is computed to be longer
in a case where all the channels are not free than in a case where
all the channels are free. In block 208, the wireless communication
apparatus is caused to reserve said at least one channel detected
to be free according to the requirement of the TXOP holder for the
second reservation period and to transmit data during said second
reservation period. The process of FIG. 2A may occur during the
same TXOP.
[0023] Referring to FIG. 2B illustrating the functionality of an
intended receiver of the TXOP, the process starts in block 210. In
block 212, a transmission request message is received in a wireless
communication apparatus on a plurality of channels at a beginning
of the TXOP. The transmission request message may be used to query
whether or not at least one of said plurality of channels is free,
and the transmission request message triggers a first reservation
period to said plurality of channels. In block 214, a second
reservation period is computed on the basis of the number of
channels detected to be free with respect to the number of said
plurality of channels on which the transmission request message was
received. As was the case in the process of FIG. 2A, the second
reservation period is computed to be longer in a case where all the
channels are not free than in a case where all the channels are
free. In block 216, the wireless communication apparatus is caused
to transmit a transmission response message as a response to the
transmission request message, wherein the transmission response
message indicates at least one channel the second wireless
communication apparatus has detected to be free, and wherein the
transmission response message triggers reservation of said at least
one channel detected to be free for the duration of the second
reservation period. Thereafter, the wireless communication
apparatus may receive data during the second reservation period and
during the TXOP.
[0024] Computation of the reservation period on the basis of the
channels that are detected to be free in both the transmitter and
the receiver in response to the RTS/CTS handshake enables
optimizing the duration of the reservation compared to a case where
the transmitter itself computes the reservation period on the basis
of channels it detects to be free. In some scenarios, at least some
of the channels the transmitter detects to be free may be occupied
in the receiver which leads to availability of less channels for
the TXOP and increased duration of the reservation period. This may
lead to under-allocation of the reservation period which is
effectively solved by the embodiments of FIGS. 2A and/or 2B. On the
other hand, if the transmitter prepares for the worst case scenario
(only the primary channel being free) with respect to the
occupation of the channels by maximizing the duration of the
reservation, this may lead to over-allocation of the reservation
period in a case where the more channels are actually free than in
the worst-case scenario. This leads to poor spectral efficiency
which is also effectively solved by the embodiments of FIGS. 2A
and/or 2B. Accordingly, such embodiments provide means for adapting
the reservation to a transmission bandwidth mismatch between the
transmitter and the receiver of the TXOP. The transmission
bandwidth mismatch refers to a mismatch between the channels the
transmitter has detected to be free and the channels the receiver
has detected to be free.
[0025] FIGS. 3 to 7 illustrate embodiments for carrying out the
adaptation of the reservation. In some embodiments, the adaptation
of the reservation period is computed in the transmitter of the
TXOP, while in other embodiments the adaptation of the reservation
period is computed in the receiver of the TXOP. It should be noted
that in some embodiments both the transmitter and the receiver may
support the adaptation of the reservation period, and the entity
carrying out the adaptation may also be adaptively determined by
the TXOP holder, for example. Therefore, some embodiments provide a
wireless communication apparatus supporting the adaptation of the
reservation period when it is the TXOP holder and when it is a
receiver of a TXOP.
[0026] Referring to FIG. 3, let us consider an embodiment where the
receiver carries out the adaptation of the reservation period. The
embodiment of FIG. 3 utilizes a probing phase during which at least
the RTS/CTS handshake is carried out. The probing phase defines a
time duration exclusive to the RTS/CTS handshake, and actual data
transmission may be performed outside the probing phase, as
illustrated in FIG. 3. In some embodiments, the probing phase
includes a period for transmitting another control message after
the CTS message, as will become apparent from the description
below. The probing phase may be carried out at the beginning of the
TXOP and/or after transmission of some data during the TXOP. The
probing phase enables the determination of available channels in
both the transmitter (the TXOP holder) and the receiver and the
determination of whether or not to carry out the data transmission
by using the channels free in both the transmitter and the
receiver. A static and a dynamic reservation type may be defined,
wherein the static reservation type may refer to proceeding with
the data transmission if all the channels indicated in the
transmission request message are free also on the receiver side.
The dynamic reservation type may refer to proceeding with the
transmission when a subset of the channels indicated in the
transmission request message is free on the receiver side. The
reservation type may be indicated in the transmission request
message. Upon gaining the TXOP, the TXOP holder transmits during a
first probing phase the RTS message on the channels that it has
detected to be free and intends to use in the TXOP for transmission
of data to the receiver, e.g. the primary to quaternary channels as
illustrated in FIG. 3. The RTS messages are addressed to the
receiver or a plurality of receivers. A separate RTS message having
the identical contents may be transmitted to the receiver on each
channel, thereby separately requesting transmission on each
channel. The RTS message may comprise a duration field defining the
duration of the NAV protection for the channels on which the RTS
message is transmitted. The NAV is verified and applied if the
receiver(s) of the RTS frame transmit the CTS message within the
CTS timeout. The CTS timeout is a duration during which all other
devices except the device which receiver address was indicated in
the RTS frame wait to receive CTS frame to RTS frame, i.e. these
devices may not start to obtain TXOP or transmit during this time.
The CTS timeout covers at least a following CTS message, and
approximately the message following the CTS message, e.g. a
CTS-to-self message described below.
[0027] Upon reception of the RTS message from the TXOP holder, the
receiver may carry out CCA procedure, or may have carried out the
CCA beforehand, and prepares the CTS message to be transmitted on
those channel(s) detected to be free in the CCA procedure. The
receiver may also take into account detected NAVs of other STAB on
the channel(s) on which the RTS was received. In this case, the
receiver detects that only the primary channel is free and, thus,
transmits the CTS message on the primary channel only. In general,
the receiver may transmit the CTS message only on those channels
for which it detects no NAV protection by the other STAB. The CTS
message may also comprise the duration field setting the duration
of the NAV protection on the channel(s) on which the CTS is
transmitted. In this case, since only the primary channel is free,
the receiver may determine that the number of free channels is too
low for carrying out the reservation of the channel(s) for the data
transmission. This may be determined from a message received from
the TXOP holder that defines whether to utilize the static or
dynamic reservation type. With respect to the dynamic reservation
type, a minimum number of free channels needed to carry out the
data transmission may be defined in the RTS message, or it may be
defined as a default value in the receiver, e.g. the number of free
channels in the receiver with respect to the number free channels
on which the RTS was received. For instance, if the RTS message has
commanded the receiver to apply a static reservation type, e.g.
commanded to reserve all resources, the receiver may compute the
extended duration of NAV for CTS frame only if all the queried
channels are sensed to be idle. If the RTS frame commands the
dynamic reservation type, e.g. command to reserve any available
resource, the receiver may determine that the TXOP proceeds to the
data transmission and extend the duration of the NAV. The reserved
duration may be scaled as function of reserved bandwidth, as will
be described below. The reservation duration may be limited by a
maximum time limit of the TXOP which may be defined by TXOPLimit
parameter for each access category (AC). In response to determining
to discontinue the reservation, the receiver may still transmit the
CTS message to enable the TXOP holder to determine, on the basis of
the CTS message received even though the data transmission is
discontinued, correct reception of the RTS message and the number
of the idle channels seen by the CTS transmitter and compute the
duration field of the CTS message to define a time duration that
ends at the same time as the NAV setting defined by the RTS
message. The duration may thus be computed from the value of the
duration field of the received RTS message as follows:
NAV CTS { = CTS_Timeout + .delta. , probing , fail = NAV RTS * 32
.mu. s , probing , success = NAV RTS - ( CTS + SIFS ) , reservation
( 1 A ) NAV RTS { .ltoreq. CTS_Timeout + .delta. , probing >
CTS_Timeout + .delta. , reservation ( 1 B ) ##EQU00001##
[0028] NAV.sub.RTS is the duration defined in the duration field of
the RTS message which may be used to trigger the probing operations
as shown in Equation (1B), CTS_Timeout is the duration during which
the CTS frame (or at least its preamble) should be received as a
response to the RTS message in order to validate the NAV protection
defined in the duration field of the RTS message, .delta. is the
duration of a subsequent CTS-to-self or a further RTS message, as
will be described below. In one embodiment, .delta. may be set to
zero. CTS is the duration of the CTS message, and SIFS (short
inter-frame space) is a guard period that may be provided between
the RTS and CTS messages and commonly used in IEEE 802.11 networks.
Then, the receiver may transmit the CTS message to the TXOP holder.
Equation 1A includes three options from which one is selected on
the basis of the command to either carry out the reservation or the
probing (Defined by the value of the duration field in the RTS
message. From the two options related to the probing, one is
selected on the basis of whether or not the number of detected
channels is sufficiently high to result in the data transmission
(explained above with respect to the static/dynamic reservation
types). If the data transmission is not carried out, the receiver
computes the NAV protection to start from the transmission of the
CTS message and end at the same time the CTS_Timeout ends (probing,
fail in Equation 1A). If the data transmission is carried out
(probing, success in Equation 1A,) the receiver may compute the NAV
protection to extend the duration indicated in the RTS message. In
this example, the duration of the NAV protection defined in the RTS
message is scaled (multiplied), although in other embodiments, the
extension may be carried out through adding a determined time
period. As illustrated in FIG. 3, the NAV protection of the RTS
message may be shorter than the CTS_Timeout, and the NAV protection
of the CTS message may either be limited by the CTS_Timeout or the
amount of extension.
[0029] In this example, the first probing phase results in the
failed probing, as only the primary channel was free. Thus, the
receiver returns the CTS message with the duration ending within
the CTS-Timeout. Upon reception of the CTS message in the TXOP
holder, the TXOP holder also determines to discontinue with the
reservation and end the first probing phase. As already mentioned,
the value of the NAV.sub.RTS parameter may be used to indicate to
the receiver of the RTS message whether the probing is being
carried out without any intention to transmit data yet or whether
the reservation is intended to cover the data transmission.
Detailed embodiments are discussed below.
[0030] Subsequently, the TXOP holder may determine to carry out
another probing phase by transmitting the RTS messages on the same
channels (channels it detects to be free). This may follow the
above-described principle, and the NAV set by the RTS message may
again cover only the probing phase. Now, the receiver detects that
the secondary channel is also free and, thus, determines to proceed
to channel reservation for the data transmission. Now, the receiver
may compute the duration of the reservation for data transmission
in the second reservation phase, e.g. to the end of the data
transmission. The receiver may now calculate the new NAV.sub.CTS as
follows:
NAV'.sub.CTS=NAV.sub.CTS+2.times.SIFS+W.times.T+ACK (2)
where W is a coefficient defined according to the number of
channels the receiver determined to be free with respect to the
number of channels on which the RTS message was received. T defines
a default duration for the data transmission when all the channels
on which the RTS was received are free. As a consequence, the
coefficient scales the duration in proportion to the decrease of
free channels. For example, when the number of actually free
channels is half of the number of channels on which the RTS message
was received, the coefficient may take the value of two. In
practice, the scalability may not be so straightforward because a
higher number of channels utilized also provides a higher MAC layer
signaling overhead and decreases the transmission power density
making the received signal to have a lower power level. Therefore,
the coefficient may also take another value, e.g. 1.5. The value of
the scaling coefficient may be determined according to the system
design and according the rate adaptation logic that selects a
modulation and coding scheme according to link conditions. ACK
defines the duration of an acknowledgment message. The computation
of the NAV'.sub.CTS may also take into account the SIFS periods
between the frames. To account for the decision whether or not to
proceed with the channel reservation, a decision may be made
whether to compute Equation (1A) and, if not all requested channels
were reserved the Equation (2) is used, or, from another point of
view, whether to omit term (2.times.SIFS+W.times.T+ACK) from
Equation (2). Equation (2) may be an alternative to the "probing
success" and/or "reservation" options of Equation (1A).
[0031] The value of the NAV'.sub.CTS is then inserted into the
duration field of the CTS message, and the CTS message is
transmitted on the channels the receiver detected to be free (the
primary and the secondary channels in this example), thereby
triggering the NAV protection to those channels in the coverage
area of the receiver. Upon reception of the CTS message, the TXOP
holder computes the remaining length of the NAV protection as
follows:
NAV.sub.S-CTS=NAV'.sub.CTS-(SCTS+SIFS) (3)
wherein SCTS defines the length of a CTS message the TXOP holder
subsequently transmits. The CTS message is addressed to the TXOP
holder itself, and such a CTS message is called CTS-to-self
message. A separate copy of the SCTS message may be transmitted on
every 20 MHz channel similarly as CTS and RTS messages. The
CTS-to-self message is arranged to comprise the remaining length of
NAV protection computed in Equation (3) so as to carry out the NAV
protection also in the coverage area of the TXOP holder. The TXOP
holder may skip the transmission of the SCTS and proceed to
transmit data to the receiver on the channels negotiated to be
free, and receives acknowledgment upon successful reception of the
data, as illustrated in FIG. 3.
[0032] FIG. 4 illustrates an embodiment utilizing the probing,
wherein the TXOP holder computes the reservation period according
to the number of commonly available channels. In this embodiment,
the TXOP holder transmits the RTS message on the channels it
detects to be free, and it sets the duration field of the RTS
message to cover the subsequent CTS message and the subsequent
message, as illustrated in FIG. 4. The subsequent message is in
this case another RTS message instead of CTS-to-self message. Upon
reception of the RTS message from the TXOP holder, the receiver
detects the free channels, computes the duration field for the CTS
message according to Equation (1A), and transmits the CTS message
to the TXOP holder on the free channels (the primary and the
secondary channel in this case, too). Upon reception of the CTS
message, the TXOP holder determines whether or not to proceed. Let
us assume that the number of commonly free channels is sufficient
and that the reservation continues. The transmitter now computes a
value for the duration field of an RTS message to be transmitted
such that it covers a subsequent, CTS message following the RTS
message, data transmission period on the commonly free channels,
and the subsequent acknowledgment period. Then, the TXOP holder
transmits the RTS message that sets the NAV in the coverage area of
the TXOP holder. Upon reception of the RTS message, the receiver
again computes the duration field for the CTS message according to
Equation (1A) and then inserts the remaining duration in the
duration field of the CTS message transmitted to the TXOP holder.
Accordingly, the NAV setting provided by the CTS message is
arranged to end at the same time with the NAV setting provided by
the RTS message. Upon reception of the CTS message in the TXOP
holder, the TXOP holder carries out the data transmission, as
described above.
[0033] FIG. 5 illustrates an embodiment without the separate
probing phase, wherein the TXOP holder adapts to the transmission
bandwidth mismatch with the receiver by recomputing the duration of
the reservation period. The TXOP holder may determine the channels
that are free and compute the duration of the reservation period on
the basis of the number of free channels. In this example, the TXOP
holder detects that primary to quaternary channels are free and,
thus, it computes the duration of the reservation period according
to the following Equation, and inserts a resulting value to the
duration field of a first RTS message transmitted to the intended
receiver:
NAV.sub.RTS=3.times.SIFS+CTS+DATA+ACK, (4)
where DATA is the transmission time of the data frame based on the
available transmission bandwidth, i.e., the number of free
channels. The NAV set in this manner is illustrated in FIG. 5 by
"RTS1". However, the receiver observes that only the primary and
secondary channels are free and, thus, transmits a CTS message only
on those channels. The receiver may compute the NAV duration
according to Equation (1A) and include it in the duration field of
the CTS message. Upon detection that the number of commonly free
channels is lower than the TXOP holder initially detected,
resulting in under-allocation of the NAV protection, the TXOP
holder determines to extend the NAV protection and recomputes the
duration of the reservation period according to the number of
commonly free channels (e.g. 2 in this example) and transmits a
second RTS message (RTS2 in FIG. 5) with the recomputed duration
according to Equation (4). Thus, the TXOP holder extends the NAV
protection appropriately, as illustrated by RTS2 in the NAV
protection line in FIG. 5. The second RTS may be transmitted only
on the channels that the receiver reported to be free. Upon
reception of the second RTS message, the receiver acknowledges the
RTS message by a second CTS message for which the NAV protection is
computed according to Equation (1A) again, thereby providing the
same NAV protection in the coverage area of the receiver, as
illustrated by CTS2 in the NAV protection line in FIG. 5. As a
consequence, this embodiment provides the TXOP holder with means
for adapting to the transmission bandwidth mismatch between the
TXOP holder and the receiver, thus avoiding the erroneous NAV
protection.
[0034] FIG. 6 illustrates two embodiments (with and without the
separate probing phase), wherein the receiver adapts to the
transmission bandwidth mismatch with the receiver by recomputing
the duration of the reservation period. In both cases, the TXOP
holder transmits the RTS message as described above, receives from
the receiver a CTS message on the commonly free channels. The CTS
message comprises the computed duration of the reservation period
that extends to cover the data transmission and, thereafter, the
TXOP holder transmits the CTS-to-self message to announce the NAV
protection in its coverage area before the actual data
transmission.
[0035] Let us first consider the embodiment with no separate
probing phase. The TXOP holder computes the duration of the NAV
protection according to the number of channels it detects to be
free according to Equation (4), and transmits the RTS message
defining the computed duration for the NAV protection. However, as
the receiver detects the transmission bandwidth mismatch, it
computes the duration for the NAV protection according to Equation
(5a) and includes the result in the CTS message transmitted on the
free channels:
NAV'.sub.CTS=3.times.SIFS+SCTS+W.times.T+ACK (5A)
NAV'.sub.CTS=2.times.SIFS+W.times.T+ACK (5B)
Note that Equation (5b) may be used instead for the case without
transmission bandwidth mismatch.
[0036] Upon reception of the CTS message, the TXOP holder may
recompute the duration for the NAV protection according to Equation
(3) and transmit the CTS-to-self message to announce the new NAV
protection in its coverage area.
[0037] With respect to the embodiment with the probing phase, the
TXOP holder may compute the duration of the NAV protection of the
RTS message to cover only the probing phase which includes the
transmission of the CTS message and the CTS-to-self message but
excluding the time for data transmission. This NAV protection is
then indicated in the RTS message, or the TXOP holder may set the
duration field of the RTS message to indicate the duration less
than the CTS_Timeout, as illustrated in FIG. 6. In the latter case,
the TXOP holder relies on the CTS_Timeout to protect the CTS
message and the subsequent CTS-to-self message. Upon reception of
the RTS message, the receiver again detects the transmission
bandwidth mismatch, computes the duration for the NAV protection
according to Equation (2) and includes the result in the CTS
message transmitted on the free channels. Upon reception of the CTS
message, the TXOP holder may recompute the duration for the NAV
protection according to Equation (3) and transmit the CTS-to-self
message to announce the new NAV protection in its coverage
area.
[0038] In some cases, the receiver may prevent the extension of the
NAV protection. For instance, if the TXOPLimit parameter prevents
the extension, the extension may be omitted, and the receiver may
respond with the CTS message without the extension of the NAV
protection. The extension of the NAV protection may be prevented
for other reasons as well.
[0039] FIG. 7 illustrates an embodiment with the probing phase
where the transmission bandwidth mismatch does not occur and where
the receiver computes the duration for the NAV protection covering
the time for data transmission. In this embodiment, the TXOP holder
transmits the RTS message on the free channels, wherein the NAV
protection provided by the RTS message covers only the probing
phase, e.g. through the CTS_Timeout. Upon reception of the RTS
message and determining that all the channels on which the RTS
message was received are free, the receiver computes the duration
of the reservation period that covers the data transmission
according to Equation (2) where the scaling coefficient W is set to
be one. The resulting value is inserted in the duration field of
the CTS message transmitted to the TXOP holder, and the TXOP
holder, transmits the CTS-to-self message with the NAV protection
computed according to Equation (3).
[0040] It should be noted that the adaptation of those channels
that the TXOP holder detected to be free but that were not commonly
free, may be arranged to avoid over-allocation of the NAV
protection by providing a mechanism where an RTS message should be
responded with the CTS message within a determined time duration in
order to affect the NAV protection defined in the duration field of
the RTS message. With respect to a third party wireless
communication apparatus detecting the RTS message transmitted from
the TXOP holder to the receiver on a given channel, if it detects
also a CTS message which is a response to the RTS message on that
channel, it applies the NAV protection of the RTS message and
avoids the channel for the duration of the NAV protection. However,
if it does not detect the CTS message in response to the RTS
message on that channel, it may reset its NAV after a determined
time period has expired after the detection of the RTS message.
This time period is shorter than the duration of the NAV
protection, and it may be
2.times.SIFS+CTS+PHY-RX-START-Delay+(2.times.SlotTime). CTS is the
duration of the CTS message, and parameters PHY-RX-START-Delay and
SlotTime (duration of a time slot) are constant values defined by
system specifications, e.g. IEEE 802.11ac specifications. THE
PHY-RX-START-Delay is the time needed to transmit a legacy 802.11a
synchronization preamble and a PLOP header. Synchronization is 16
microseconds and PLOP header 4 microseconds.
[0041] As mentioned above, an apparatus according to an embodiment
of the invention supports the adaptation of the reservation period
both when it is the TXOP holder and when it is the receiver. For
the purpose of controlling which party carries out the adaptation
on the basis of commonly free channels, one may use the duration
field of the RTS message to carry an implicit command indicating
whether or not the receiver of the RTS message should compute the
reservation period. As mentioned above, the duration field of the
RTS message is set to cover at least the subsequent CTS message. In
the IEEE 802.11ac system, the RTS message inherently sets the NAV
protection at least for the duration of the CTS message, e.g. the
above-mentioned duration
2.times.SIFS+CTS+PHY-RX-START-Delay+(2.times.SlotTime). During this
time, all STAB except the receiver of the RTS frame wait for
detection of the CTS frame. It may be assumed that this duration is
at least 62 .mu.s. The delay after which the channel access may be
performed may only be increased and, therefore, providing the
duration field with a value below 62 (or 60) .mu.s has no function
with respect to the channel reservation, and such values may be
used as control values for another purpose, e.g. to indicate which
one of the TXOP holder and the receiver should compute the duration
of the reservation period. In an embodiment, a value of the
duration field below 62 (or generally a determined value) commands
the receiver to compute the duration of the reservation period for
the data transmission, e.g. one of the embodiments of FIGS. 3, 6,
and 7. On the other hand, a value of the duration field above 62
(or generally the determined value) informs the receiver that the
TXOP holder computes the duration of the reservation period for the
data transmission, e.g. one of the embodiments of FIGS. 4 and 5.
The duration for probing may be communicated by adding a constant
extra time to duration field of the RTS frame. For instance, the
constant extra time may be 100 microseconds or the value of the
CTS_Timeout parameter. In this embodiment, the receiver that
formulates the CTS message first decreases the extra constant time
when calculating the duration value from the value of the duration
field of the RTS message. From another point of view, a value of
the duration field within a first range commands the receiver to
compute the reservation period, while a value of the duration field
within a second range not overlapping with the first range informs
the receiver that the TXOP holder computes the reservation period.
From yet another point of view, a first value of the duration field
commands the receiver to compute the reservation period, while a
second value different from the first value informs the receiver
that the TXOP holder computes the reservation period. On the basis
of the value of the duration field, the receiver may then execute
an appropriate procedure according any above-described
embodiment.
[0042] Let us assume that a determined value of the duration field
of the RTS message configured the receiver to compute the
reservation period for the data transmission, e.g. 60, and that
there is no transmission bandwidth mismatch which means that all
the channels on which the RTS message was received are commonly
free channels (see FIG. 7). Then, the receiver may be configured to
utilize a Default Reservation Step parameter defined by the
specifications or configured internally in the BSS to scale the
value of the duration field. The value of the Default Reservation
Step may be 16 or 32 .mu.s, for example. In the case of no
transmission bandwidth mismatch, the receiver may simply multiply
the value of the duration field of the RTS message with the Default
Reservation Step parameter instead of computing Equation (2). For
example, multiplication of 60 by 16 .mu.s results in the
reservation period of 960 .mu.s. On the other hand, if only half of
the channels on which the RTS was received are commonly free
channels, the receiver may scale the value of the duration field
accordingly. For example, if only half of the channels are commonly
free, the duration of the reservation may be computed as 60*16
.mu.s*2=1,92 ms (see Equation (1A), probing success).
[0043] Similarly, the apparatus according to an embodiment of the
invention may support operation with and without the probing phase,
wherein the presence or absence of the probing phase may also be
defined by the TXOP holder by setting the value of the duration
field of the RTS message appropriately. A short duration (within a
determined range) indicates that only the RTS/CTS handshake is
protected and that the protection is confined within the probing
phase. In addition, the TXOP holder has the option to continue or
discontinue with medium reservation while the receiver has the
capability to extend NAV protection according to Equation (2). On
the other hand, a long duration (within another range over the
shorter range) indicates that the protection extends to the time
for data transmission and no separate probing phase is carried out.
A long duration may range from 150 .mu.s or a few hundreds of .mu.s
to a few ms, e.g. 3 ms.
[0044] The concept of the embodiments utilizing the probing phase
may be generalized into processes executed in the TXOP holder and
in the receiver as illustrated by flow diagrams of FIGS. 8A and 8B,
respectively. The TXOP is separated into a probing phase and data
transmission following the probing phase, as illustrated by the
dashed line in FIG. 8A. Referring to FIG. 8A illustrating the
operation of a wireless communication apparatus functioning as the
TXOP holder, the process starts in block 800. In block 802, the
wireless communication apparatus is caused to transmit during the
probing phase a transmission request message to a second wireless
communication apparatus on a plurality of channels. The
transmission request message is used to query whether or not at
least one of said plurality of channels is free, and the
transmission request message triggers a first reservation period to
said plurality of queried channels. The first reservation period
may be confined to the probing phase, e.g. it does not extend to
data transmission. In block 804, a transmission response message is
received as a response to the transmission request message during
the probing phase, wherein the transmission response message
indicates at least one channel the second wireless communication
apparatus has detected to be free. In block 806, the duration of a
second reservation period is determined on the basis of the
received transmission response message, wherein the second
reservation period extends to the time for data transmission and is
longer in a case where at least one of said plurality of queried
channels is detected not to be free than in a case where said
plurality of queried channels are all detected to be free. In block
808, the wireless communication apparatus is caused to reserve said
at least one channel detected to be free for the second reservation
period and to begin data transmission.
[0045] Referring to FIG. 8B illustrating the operation of a
wireless communication apparatus functioning as the receiver during
the TXOP, the process starts in block 810. In block 812, a
transmission request message is received during the probing phase
on a plurality of channels, wherein the transmission request
message is used to query whether or not at least one of said
plurality of channels is free, and wherein the transmission request
message triggers a first reservation period to said plurality of
channels. As mentioned above, the first reservation period may be
confined to the probing phase. In block 814, the duration of a
second reservation period is determined during the probing phase,
wherein the second reservation period extends to the time for data
transmission and is longer in a case where at least one of said
plurality of channels is detected not to be free than in a case
where said plurality of channels are all detected to be free. In
block 816, the wireless communication apparatus is caused to
transmit a transmission response message as a response to the
transmission request message during the probing phase, wherein the
transmission response message indicates at least one channel the
second wireless communication apparatus has detected to be free.
Blocks 814 and 816 may be executed in any order depending on
whether the TXOP holder or the receiver computes and indicates the
duration of the second reservation period to the other party.
[0046] The concept of the embodiments where the duration of the
reservation period is determined on the basis of the RTS/CTS
handshake and optionally utilizing the probing phase may be
generalized into processes executed in the TXOP holder and in the
receiver as illustrated by flow diagrams of FIGS. 9A and 9B,
respectively.
[0047] Referring to FIG. 9A illustrating the operation of a
wireless communication apparatus functioning as the TXOP holder,
the process starts in block 900. At a beginning of a transmission
opportunity in block 902, the wireless communication apparatus is
caused to transmit a transmission request message to a second
wireless communication apparatus on a plurality of channels,
wherein the transmission request message is used to query whether
or not at least one of said plurality of channels is free, and
wherein the transmission request message triggers a reservation
period to said plurality of channels. In block 904, a transmission
response message is received as a response to the transmission
request message, wherein the transmission response message
indicates at least one channel the second wireless communication
apparatus has detected to be free. In block 906, a new duration of
the reservation period is derived on the basis of a transmission
bandwidth mismatch between the number of channels detected to be
free with respect to the number of said plurality of channels on
which the transmission request message was transmitted, wherein the
new duration of the reservation period extends to the time for data
transmission and is longer in a case where at least one of said
plurality of channels is detected not to be free than in a case
where said plurality of channels are all detected to be free. In
block 908, the wireless communication apparatus is caused to
transmit a message that defines the derived duration for reserving
said at least one channel detected to be free and transmitting data
during said reservation period on said at least one channel
detected to be free.
[0048] Referring to FIG. 9B illustrating the operation of a
wireless communication apparatus functioning as the receiver during
the TXOP, the process starts in block 910. In block 912, a
transmission request message is received on a plurality of channels
at a beginning of the TXOP. The transmission request message is
used to query whether or not at least one of said plurality of
channels is free, and the transmission request message triggers a
reservation period to said plurality of channels. In block 914, a
new duration of the reservation period is derived on the basis of a
transmission bandwidth mismatch between the number of channels
detected to be free with respect to the number of said plurality of
channels on which the transmission request message was received,
wherein the new duration of the reservation period extends to the
time for data transmission and is longer in a case where at least
one of said plurality of channels is detected not to be free than
in a case where said plurality of channels are all detected to be
free. In block 916, the wireless communication apparatus is caused
to transmit a transmission response message as a response to the
transmission request message, wherein the transmission response
message indicates at least one channel the second wireless
communication apparatus has detected to be free and the new
duration of the reservation period. Thereafter, data may be
received during the reservation period and during the TXOP.
[0049] FIG. 10 illustrates an embodiment of an apparatus comprising
means for carrying out the above-mentioned functionalities of the
TXOP holder and/or the receiving STA. The apparatus may be a
communication apparatus of an IEEE 802.11 network or another
wireless network, e.g. an AP or STA. The communication apparatus
may be a computer (PC), a laptop, a tabloid computer, a cellular
phone, a palm computer, a fixed base station operating as the AP,
or any other communication apparatus. In another embodiment, the
apparatus is comprised in such a communication apparatus, e.g. the
apparatus may comprise a circuitry, e.g. a chip, a processor, a
micro controller, or a combination of such circuitries in the
communication apparatus.
[0050] The apparatus may comprise a communication controller
circuitry 10 configured to control the communications in the
communication apparatus. The communication controller circuitry 10
may comprise a control part 14 handling control signaling
communication with respect to transmission, reception, and
extraction of control frames including the transmission request
messages and the transmission response messages, as described
above. The communication controller circuitry 10 may further
comprise a data part 16 that handles transmission and reception of
payload data during transmission opportunities of the communication
apparatus (transmission) or transmission opportunities of other
communication apparatuses (reception). The communication controller
circuitry 10 further comprise a reservation period computation
circuitry 11 configured to carry out the computation of the
reservation period on the basis of the commonly free channels
detected during the RTS/CTS handshake. The algorithm used for the
computation of the reservation period may be controlled by the
communication controller circuitry on the basis of whether or not
the apparatus functions as the TXOP holder or the receiver.
Additional criteria may be used to select the algorithm, e.g.
whether or not to utilize the probing phase. Detailed embodiments
related to the computation of the reservation periods, according to
which the reservation period computation circuitry may operate, are
described above.
[0051] The circuitries 11 to 16 of the communication controller
circuitry 10 may be carried out by the one or more physical
circuitries or processors. In practice, the different circuitries
may be realized by different computer program modules. Depending on
the specifications and the design of the apparatus, the apparatus
may comprise some of the circuitries 11 to 16 or all of them.
[0052] The apparatus may further comprise the memory 20 that stores
computer programs (software) configuring the apparatus to perform
the above-described functionalities of the communication device.
The memory 20 may also store communication parameters and other
information needed for the wireless communications. The apparatus
may further comprise radio interface components 30 providing the
apparatus with radio communication capabilities within the BSS and
with other BSSs. The radio interface components 30 may comprise
standard well-known components such as amplifier, filter,
frequency-converter, (de)modulator, and encoder/decoder circuitries
and one or more antennas. The apparatus may further comprise a user
interface enabling interaction with the user of the communication
device. The user interface may comprise a display, a keypad or a
keyboard, a loudspeaker, etc.
[0053] In an embodiment, the apparatus carrying out the embodiments
of the invention in the communication apparatus comprises at least
one processor and at least one memory including a computer program
code, wherein the at least one memory and the computer program code
are configured, with the at least one processor, to cause the
apparatus to carry out the steps of any one of the processes of
FIGS. 2A, 2B, 8A, 8B, 9A, and 9B. In further embodiments, the at
least one memory and the computer program code are configured, with
the at least one processor, to cause the apparatus to carry out any
one of the embodiments related to processing the reservation period
on the basis of the RTS/CTS handshake, as described above in
connection with FIGS. 2A to 9B. Accordingly, the at least one
processor, the memory, and the computer program code form
processing means for carrying out embodiments of the present
invention in the wireless communication apparatus.
[0054] As used in this application, the term `circuitry` refers to
all of the following: (a) hardware-only circuit implementations,
such as implementations in only analog and/or digital circuitry,
and (b) to combinations of circuits and software (and/or firmware),
such as (as applicable): (i) a combination of processor(s) or (ii)
portions of processor(s)/software including digital signal
processor(s), software, and memory(ies) that work together to cause
an apparatus to perform various functions, and (c) to circuits,
such as a microprocessor(s) or a portion of a microprocessor(s),
that require software or firmware for operation, even if the
software or firmware is not physically present.
[0055] This definition of `circuitry` applies to all uses of this
term in this application. As a further example, as used in this
application, the term "circuitry" would also cover an
implementation of merely a processor (or multiple processors) or
portion of a processor and its (or their) accompanying software
and/or firmware. The term "circuitry" would also cover, for example
and if applicable to the particular element, a baseband integrated
circuit or applications processor integrated circuit for a mobile
phone or a similar integrated circuit in server, a cellular network
device, or other network device.
[0056] The processes or methods described in FIGS. 2A to 9B may
also be carried out in the form of a computer process defined by a
computer program. The computer program may be in source code form,
object code form, or in some intermediate form, and it may be
stored in a transitory or a non-transitory carrier, which may be
any entity or device capable of carrying the program. Such carriers
include a record medium, computer memory, read-only memory,
electrical carrier signal, telecommunications signal, and software
distribution package, for example. Depending on the processing
power needed, the computer program may be executed in a single
electronic digital processing unit or it may be distributed amongst
a number of processing units.
[0057] The present invention is applicable to wireless
telecommunication systems defined above but also to other suitable
telecommunication systems. The protocols used, the specifications
of mobile telecommunication systems, their network elements and
subscriber terminals, develop rapidly. Such development may require
extra changes to the described embodiments. Therefore, all words
and expressions should be interpreted broadly and they are intended
to illustrate, not to restrict, the embodiment. For example, the
receiver of the RTS/CTS handshake may be another apparatus than the
intended receiver of the data transmission, and the TXOP holder may
transmit the data to another apparatus. It will be obvious to a
person skilled in the art that, as technology advances, the
inventive concept can be implemented in various ways. The invention
and its embodiments are not limited to the examples described above
but may vary within the scope of the claims.
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